For example, Japanese Patent Laid-Open No. 2008-49652 proposes a resin molding method for obtaining a high-grade metallic appearance according to the related art, in which welds or orientation lines in a resin flow pattern are not formed on a design surface by glittering materials containing metallic compounds including aluminum, mica, and glass flakes. The technique of the resin molding method prevents a flow of molten resin into a cavity between dies from first reaching a shape affecting the design surface, so that the molten resin flowing to the design surface fills the cavity without being interrupted.
FIG. 12A is a front view showing the backside of the design of a resin molded article described as an invention on pages 5 to 8 and FIGS. 2, 3, and 7 of Japanese Patent Laid-Open No. 2008-49652. FIG. 12B is a sectional view taken along line A-A of FIG. 12A. FIG. 13A is a front view showing the backside of the design of a resin molded article described as a product of the related art in Japanese Patent Laid-Open No. 2008-49652. FIG. 13B is a sectional view taken along line B-B of FIG. 13A.
As shown in FIGS. 13A and 13B, in a resin molded article 100 of the related art, a rib 102 extending along the width of the resin molded article 100 and a rib 103 extending along the length of the resin molded article 100 directly protrude from the backside of a design surface 101. Molten resin is injected from a gate 104, which serves as a resin inlet, into a cavity formed by dies for fabricating the resin molded article 100 of the related art, and the molten resin flows to the design surface 101 from the rib 102 and the rib 103 and forms orientation lines in a resin flow pattern on the design surface 101, adversely affecting the design surface 101.
FIGS. 12A and 12B show a resin molded article 110 described as the invention of Japanese Patent Laid-Open No. 2008-49652, in which a rib 113 is widely extended on the backside of a design surface 111 along the length of the resin molded article 110 with ribs 112a, 112b, 112c, and 112d protruding from the backside of the design surface 111 so as to extend in the rib 113 along the width of the resin molded article 110. The rib 113 has a clearance from the design surface 111 except for the ribs 112a, 112b, 112c, and 112d. Thus in the resin molded article 110, molten resin injected into a cavity from a gate 114, which serves as a resin inlet in dies, is first applied to the design surface 111 through the rib 112a, and then the molten resin is applied to the rib 113 through the rib 112a. In this case, the molten resin applied from the rib 112a forms the rib 113; meanwhile, the molten resin passes through the thin and narrow ribs 112b, 112c, and 112d that are raised against the flowing direction, so that the molten resin cannot flow in a direction from the rib 113 to the design surface 111. Thus in the process of applying the molten resin toward the design surface 111, the flow of resin to the design surface 111 is interrupted (i.e., no resin flow joining from other points), which prevents welds and orientation lines in a resin flow pattern on the design surface 111.
As shown in FIG. 14, compounds 142 in a molding resin 141 are mostly arranged in certain directions by resin flows 143 and 144 during molding. At an interface 145 between the resin flows in different directions in a resin molding space in the dies, the directions of resin flows rapidly change, accordingly varying the flows of the compounds 142. The orientation lines are changes in the arrangement of the compounds 142 at the interface. Generally, such orientation lines occur on the appearances of resin molded articles made of resin materials containing metallic compounds (aluminum, mica, and glass flakes) that add metallic luster to the surfaces of the resin molded articles.
A high-grade metallic appearance can be obtained by other methods using glittering materials containing metallic compounds including aluminum, mica, and glass flakes, without forming welds or orientation lines in a resin flow pattern on a design surface. For example, such resin molding methods are proposed in pages 2 and 3 and FIGS. 1 to 4 of Japanese Patent Laid-Open No. 8-72067 and pages 2 and 3 and FIG. 3 and so on of Japanese Patent Laid-Open No. 2000-301583. In these resin molding methods, an uneven part is eliminated from the cavity of dies because an uneven part may divide or block a resin flow in a flow path when molten resin is injected into the cavity of dies. These methods can prevent welds and orientation lines in a resin flow pattern on a design surface.
FIG. 15 shows the resin molding method of Japanese Patent Laid-Open No. 8-72067. In this resin molding method, a boss portion is formed as a projection on a product (resin molded article) but as a recessed portion on a die. As shown in FIG. 15, a movable pin 122 is slidably disposed in a die (lower die) 121 to form the boss portion. Further, an elastic member 124 urging the movable pin 122 upward is provided on the underside of the movable pin 122. Reference numeral 123 in FIG. 15 denotes the other die (upper die). The dies 121 and 123 form a cavity 125 to be filled with resin. In this configuration, when molten resin passes through a point to be formed into the boss portion, the die 121 does not have any recessed portions facing the cavity 125. After the cavity 125 is filled with the molten resin, the pressure of the molten resin slides the movable pin 122 against the elastic member 124 so as to form a recess on the die 121. The boss portion on the product (resin molded article) is formed thus.
According to the resin molding method, even in the case where a design surface is formed to face, e.g., the other die (upper die) 123 in the cavity 125, a molten resin flow along the design surface is not disturbed because any recessed portions facing the cavity 125 are not provided on the die 121. These actions can obtain a product shape without forming welds or orientation lines in a resin flow pattern on the design surface.
FIG. 16 shows the resin molding method of Japanese Patent Laid-Open No. 2000-301583. Also in this resin molding method, a boss portion is formed as a projection on a product but as a recessed portion on a die. In the resin molding method of FIG. 16, however, movable pins 132 capable of protruding from a die (lower die) 131 are slidably disposed to form boss portions. Below the movable pins 132, drive units 134 are provided that protrude the movable pins 132 into a cavity 133 from the die 131. Reference numeral 135 in FIG. 16 denotes the other die (upper die) that forms the cavity 133 with the die (lower die) 131 during molding.
In this configuration, when molten resin passes through a point to be formed into the boss portion, the movable pins 132 are not protruded into the cavity 133. After the cavity 133 is filled with the resin, the movable pins 132 are protruded into the cavity 133 by the driving units 134 to form recessed portions on a resin molded article. Thus even in the case where a design surface is formed to face the other die (upper die) 135 in the cavity 133, a molten resin flow along the design surface is hardly disturbed, achieving a product shape without forming welds or orientation lines in a resin flow pattern on the design surface.